Two people were seen to be lying within Old Palace Yard, immediately outside Westminster Hall.

A witness reported: “We heard a loud bang, lots of shouting and men running around.
Someone rushed through, attacked a policeman.
“He appeared to be carrying a knife or a gun. We then heard gunfire, five or six rounds.
“The man approaching one of the police officers with a knife.”

Another witness told Sky News a man was seen walking towards a policeman with a knife in his hand, having already assaulted another policeman.

A medical helicopter has landed outside the Houses Parliament to treat victims.